What dust are you using? Does she sit right at the water bottle and get wet? Mats should be tugged out so they dont get larger. It wont hurt the chin but dont be surprised if the kack at you
You might also find that the fur is matting if the chin is chewing it. I had a rescue that was fur chewing and had horrible mats. I just plucked them and gave her a good combing and lots of dust baths.
Where are the mats located on the body? I ask as you mentioned sticky, which isn't entirely common with mats. Likewise, a picture may help assess the situation better. Regardless, as dreamlite mentioned, mats need tugged out before they get bigger.